A dual-band shared aperture antenna array for phased array system operated in Ku/Ka-bands is proposed in this paper. By judiciously designing the geometrical structure and parameters, compact and integrated antenna elements are proposed to achieve the maximum scanning angle without the grating lobes phenomenon. The patch-dipole antenna elements operating in Ku-band and microstrip patch antenna elements operating in Ka-band are designed and fabricated utilizing a four-layer lamination substrate. Metal shielding vias are introduced to suppress the coupling between the antenna elements operating in different bands, meanwhile, defected ground structure is introduced to eliminate the scan blindness effect and improve the beam scanning range effectively. The proposed antenna array has 208 Ku-band elements and 832 Ka-band elements distributed in the shared aperture with a diameter of 200 mm. Measured results show that the proposed antenna array has a broad impedance bandwidth of 10.7% in Ku-band and 9.1% in Ka-band, meanwhile it has a relatively wide scanning angle ranging from −45 • to +45 • with low gain decrease and side lobe level. The proposed phased array antenna has potential application in a radar system, mobile communication system, and so on.